Disposable absorbent articles are broadly available and consumers are used to a high performance for the collecting and retaining of menses (in the case of sanitary napkins or panty liners) or for the collecting and retaining urine and fecal material (in the case of e.g. disposable diapers). However, consumers do not only expect a superior absorbency behavior, but place more and more emphasis on the wearing comfort of such articles, and namely on the dryness of those articles.
Typically, such articles comprise multiple absorbent members, at least one member being primarily designed to store liquid, and at least one other member primarily designed to acquire and/or distribute liquid.
At least the storage member will often comprise super-absorbent material, which is admixed with the traditionally used pulp fiber material. Such super-absorbent materials can absorb many times (e.g. 10, 20 or 30 times) their own weight and are therefore very helpful when designing an article of improved fluid handling properties. Many recent products employ higher and higher concentrations of super-absorbent materials, that is concentrations in excess of 50% of the total weight of the storage member. These products achieve a high absorbing capacity with a very thin storage member and are thereby typically overall thin products. While super-absorbent materials can store very large amounts of liquid, they are often not able to distribute the liquid from the point of impact to more remote areas of the absorbent article and to acquire the liquid as fast as it may be received by the article.
For this reason acquisition members are used, which provide for the interim acquisition of large amounts of liquid and which often also allow for the distribution of liquid. Thereby the acquisition member plays a key role in using the whole absorbent capacity provided by the storage member.
An exemplary state of the art absorbent article, namely a sanitary napkin, is disclosed in WO 00/51651. The so-called “secondary topsheet” primarily provides for the liquid acquisition and distribution. The storage member is provided in the form of a core that can contain a high portion of super-absorbent polymer material.
State of the art absorbent articles in the form of disposable diapers are disclosed in the following co-pending U.S. application Ser. Nos. 10/423,425 and 10/776,851. The storage member of these articles may contain more than 50 weight-percent of super-absorbent polymer material, even more than 80% and in some embodiments even about 100% of the super-absorbent polymer material. While these articles are designed to have excellent fluid handling and fluid storage behavior, they may sometimes not be as comfortable to wear as some consumers would like it, namely those consumers interested in a premium product.
For achieving excellent fluid handling and fluid storage properties the respective storage members use super-absorbent materials, which are selected mostly with an emphasis on fluid handling properties. For example EP 304319 B1 (Goldman et al.) discloses the benefits of a relatively narrow distribution of the particle size of the super-absorbent polymers. The respective articles will preferably not comprise many fines, but relatively coarse particles. EP 752892 B1 (Goldman et al.) discloses an absorbent structure, which uses concentrations of super-absorbent particles in access of 60% and teaches to use super-absorbent particles of a relatively high porosity.
Materials suitable to meet the above outlined requirements for a liquid acquisition member must meet these requirements not only in standard or ideal conditions, but in a variety of conditions, namely at different temperatures and pressures.
Those different temperatures and pressures are encountered, for example, under the in-use conditions. In use, the temperature at which the acquisition layer must operate depends both on the body temperature of the wearer and on the ambient temperature (which is typically below the body temperature, but in some climates can also exceed the body temperature). Most pressure on the liquid acquisition layer is typically exerted when a wearer is sitting. The temperature depends on the body weight of the wearer but can also largely depend on the surface on which the wearer sits.
Other relevant conditions regarding the performance of liquid acquisition layer are those conditions of storage and transport. In one aspect, this includes the conditions under which the diapers once produced are stored and transported. Typically a diaper package exerts some compressive force onto the diaper and, depending largely on the country of marketing, may undergo a rather large range of temperatures, before being delivered to the consumer. It is important, that the liquid acquisition layer irrespective of its storage and transport history recovers to a condition, which allows for optimal liquid handling. In a second aspect, the transport and storage conditions of the material to be formed into a liquid acquisition layer before the manufacturing of the diaper are also relevant. Very often, these materials are provided as roll stock materials. To allow for economic handling and transport the material is wound onto a roll under some pressure. The respective rolls my also be stored over a relatively long period of time, and while being stored or transported be exposed to a large variety of ambient temperatures. Of course, irrespective also of the storage and transport history a material may have undergone in these earlier stages of its lifetime, a material must recover, such that optimal liquid handling performance is achieved when the material is ultimately used as a liquid acquisition layer and expected to perform in a diaper.
U.S. Pat. No. 5,997,980 (Matoba et al.) discloses the use of hollow polyester fibers for providing a nonwoven material, the hollow polyester fibers having a relatively large hollow volume of 40% to 85%. The material is said to have a high resistance to compression and a high recovery from compression.
EP 1 032 345 B1 discloses a fluid acquisition-transfer layer for an absorbent article which comprises a mixture of heat-shrunk, spiralized, thermoplastic multi-component, preferably, bi-component, functional fibers. WO 03/048440 (Brown et al.) discloses the use of similar fibers for a non-woven fabric for a use in personal care absorbent articles, the fibers namely being single polymer, helically crimped fibers.
WO 98/22279 (Flohr et al.) discloses acquisition layers for improved liquid handling in absorbent articles. As a preferred fluid handling material fibrous materials, which are preferably carded are disclosed. These fibers are chemically bonded by a resin. The disclosed resins are more hydrophilic than the base polymer and are non-uniformly distributed in the fluid handling material throughout the thickness (z-direction). The fluid handling material is designed to achieve an acquisition performance of less than 2 seconds for the third impacting gush of liquid. The disclosed acquisition layer materials are disclosed as being easy to handle and easy to transport without requiring a large volume.
EP 149 880 (Kwok) discloses non-woven webs of synthetic fibers consolidated by means of carboxylated styrene-butadiene lattices, and disposable articles make therefrom. The obtained non-wovens are described as having improved wet tensile and elongation properties.
US 2003/0105190 (Diehl et al.) discloses a latex for utilization as a binder for nonwoven applications and a process for preparing such latex. The latex is essentially of the styrene-butadiene type.
The prior art comprises many examples of attempts to improve the rheology of adhesives, typically hot-melt adhesives and also hydrogels, allowing for better application of the adhesive materials or for better adhesion. For example, WO 98/28022 (P. Coles et al.) discloses topical adhesive for the application of functional articles. The adhesive has an elastic modulus G′ at a temperature of 37° C. and a viscous modulus G″ at 37° C. The patent application discloses optimal ranges and relationships for G′ and G″. WO 02/78756 discloses a hydrogel adhesive comprising a weak-acid monomer, and having an elastic modulus G′ at 25° C. in the range of 2000 pa to 6000 pa.
It is one objective of the present invention to provide an absorbent article, which has improved liquid handling characteristics as compared to the above disclosed articles.
Moreover, it is an objective of the present invention to provide fluid acquisition layers for improved liquid handling characteristics, namely for use with storage layer comprising a high concentration of super absorbent polymers.
In one further important aspect it is an objective of the present invention to provide an article, which is more comfortable to wear, and which in particular provides superior dryness.